1. Field of the Invention
This invention relates to apparatus for checking the operation of a plurality of liquid sprays, especially for use in a continuous casting apparatus. The invention also relates to the continuous casting apparatus itself.
The invention will be described below mainly in connection with its application in a continuous casting machine. Nevertheless the invention may be applied in checking the functioning of liquid sprays which are incorporated in other installations where an object is moved in a path past the sprays, such as for example a rolling mill.
2. Description of the Prior Art
A continuous casting machine is used in the iron and steel industry for the conversion of liquid steel into a continuous slab for example 2,000 mm wide and 250 mm in thickness. The molten steel is cast into a mould which opens vertically downwardly into a track formed by a plurality of pairs of rolls. As it leaves the water-cooled mould, the slab already possesses a solidified skin; from the mould it is led through the track supported by the rolls and is intensively cooled by water sprays between the rolls. The thickness of the skin of the slab thus increases until finally the residual molten material in the heart of the slab has solidified. Thereafter the slab is divided.
When the continuous casting process is restarted for a new charge, a so-called starting chain or dummy bar is passed through the machine, at the head of the new slab.
Usually the roll track starts vertically and turns through 90.degree. underneath the mould into a horizontal and straight portion. At the transition to this straight portion, the cast slab is pressed flat and subsequently is subjected to further cooling in the straight portion, so that the cast slab emerges horizontal and flat.
Continuous casting apparatus of this kind is known in the art, and further description is unnecessary.
With continuous casting machines designed for the casting of slabs with dimensions of 2,000 mm and 250 mm as mentioned above, the double roll track may typically comprise 50 to 100 pairs of rolls. Between each adjacent rolls on one side of the track there are 10 to 15 cylindrical aperture spray nozzles located on a support and distributed uniformly across the width of the track. In the following the entire spray support and the spray nozzles which it carries will be termed the spray system.
One major problem with known continuous casting machines is achieving correct operation of the spray systems. It may be that the location of a spray is not correct, for example the pipe to which the spray is connected is not correctly aligned or this pipe is bent, so that the original correct position of the spray has been lost. The result of this can be that the liquid is directed wholly or partially onto one of the two rolls between which the spray is located, instead of onto the slab surface. This results in wear of the expensive roll. It can also happen that the nozzles, as a result of particles entrained by the cooling water or lime deposits, become wholly or partially blocked. In all these cases the sprays do not function properly. The resultant irregular cooling of the slab surface can give rise to poor quality output, which is noticed only after some time has elapsed, when the slab is being subjected to further processing; in principle then all steel cast after the sprays ceased to function correctly is subject to the same shortcomings. If there is a larger concentration of inefficiently operating sprays and, consequently a delay in the solidification process, the skin of the slab can locally be too weak to retain the liquid steel and breakouts can occur. These result in breakdown of the continuous casting machine and loss of production.
One approach to solution of this problem which has been considered is to provide the supply pipe to each spray with a flow meter, in order to establish whether a spray is functioning and, if it is, how much liquid is being sprayed. This however will not detect a skew position of the spray or irregular spraying over the sprayed ingot.
It is also possible as a preventive measure regularly to replace all sprays in the double roll track by efficient sprays and to align the sprays. This however requires an inordinately long stoppage time during which the machine is out of service, with loss of production. Furthermore, information is not given as to whether the spray system is in good condition i.e. whether the cast slab is being efficiently cooled and to what extent the condition of the spray system is deteriorating during operation.
To avoid the problem of blockage of the nozzles by particles in the water or by deposition from the water, it has been proposed to use relatively large slot-shaped apertures in the nozzles, but these have the disadvantage that uniformity of spraying is difficult to achieve. Also the problem of misalignment of the sprays is not avoided. The description of the present invention in this specification is mainly directed to sprays having cylindrical nozzle apertures, though the invention is applicable to sprays having any shape of aperture.
Visual inspection of the operation of the sprays is possible, but is naturally slow, arduous and of insufficient precision.
Japanese published patent application no. 50-97379 (1975) proposes the use of a checking apparatus for the cooling sprays of a continuous casting machine, which apparatus comprises a carriage which is moved through the roll track by the dummy bar. The carriage carries a small number of "pressure-converting elements" (six are shown on each side) which are moved to and fro transversely of the carriage while the carriage is being moved through the roll track. These pressure converting elements are intended to measure the water spray pressure. It is stated that it is necessary for the elements to be moved to and fro, though elsewhere there is a statement that the number of elements may be increased so that they need not be moved. No details of the pressure-converting elements are given.
It is believed that the apparatus described in this Japanese patent application has not been developed successfully into an operational state. One reason for this may be that a device intended to measure the pressure exerted by sprayed water has to be extremely sensitive, and no such device suitable for operation in rugged conditions is known. The pressure of the sprayed water is as low as 40 Pascals, which is less than half the barometric pressure difference between the upper, inlet end of the roll track and the lower, horizontal outlet section. It seems that pressure-sensing devices are of inadequate sensitivity and are too slow in operation, for the present purpose. Additionally, the use of only six sensors, as illustrated in the Japanese application would produce insufficient information for the checking of a large number of sprays, unless perhaps the sensors are moved, as proposed in the Japanese application. Such movement however makes the measurement operation slow and technically complex.